Transcript Object-Oriented Software Development

Introduction to Software Engineering
Somnuk Keretho, Assistant Professor
Department of Computer Engineering
Faculty of Engineering, Kasetsart University
Email: [email protected]
URL: http://www.cpe.ku.ac.th/~sk
Outline of this presentation
•
•
•
•
•
•
Scope of Software Engineering
Object-Oriented Software Development
Software Process
Software Life-Cycle Models
Object Orientation
Software Quality Assessment
Reference to Chapter 1/2/3 of “Software Engineering with JAVA”, S.R. Schach, McGraw-Hill, 1997.
2
Scope of Software Engineering
• Software engineering is a discipline whose aim
is the production of fault-free software, that is
delivered on time, within budget, and satisfies
the user’s needs.
3
Scope of Software Engineering
• Historical Aspects:
– 1967, a NATO group coined the term “Software
Engineering”
– 1968 NATO Software Engineering Conference
concurred that “Software production should be an
engineering-like activity”.
– Using philosophies and paradigms of established
engineering disciplines to solve “Software Crisis: that
the quality of software was generally unacceptably low
and that deadlines and cost limits were not being met”.
4
Scope of Software Engineering
• Economic Aspects
– Software Engineering v.s. Computer Science
• The computer scientist investigates several ways to produce
software, some good and some bad.
• But the software engineer is interested in only those techniques
that make sound economic sense.
For example: A coding technique that can execute very
efficiently but with higher maintenance cost may not be a good
choice.
5
Scope of Software Engineering
• Maintenance Aspects
– Software Life Cycle / Software Process
•
•
•
•
•
•
•
Requirements Phase
Specification (Analysis) Phase
Planning Phase
Design Phase
Implementation Phase
Integration Phase
Maintenance Phase (highest cost among all these phases)
– Corrective, Perfective, and Adaptive Maintenance
• Retirement
6
Scope of Software Engineering
Maintenance is so important, a major aspect of software engineering
consists of techniques, tools, and practices that lead to a reduction in
maintenance cost.
Maintenance
67%
Requirement 2%
Specification 4%
Planning 1%
Design 6%
Module Coding 5%
Module Testing 7%
Integration 8%
Maintenance 76%
Approximate relative costs of
the phases of the software life cycle.
7
Scope of Software Engineering
• Specification and Design Aspects
– Software professionals are humans, and humans can
make error.
– The fact that so many faults are introduced early in the
software life cycle, highlights another important aspects
of software engineering, namely, techniques that yield
better specifications and designs.
• For example, reducing specification and design faults by 10%
will reduce the overall number of faults by 6-7%.
8
Scope of Software Engineering
• Team Programming Aspects
– Most software being developed and maintained by a
team of software engineers
– Scope of software engineering must also include
techniques for ensuring that teams are properly
organized and managed.
• For example, team programming leads to interface problems
among code components and communication problems among
team members.
9
Scope of Software Engineering
• Several techniques have been suggested to help solve the
software crisis.
– ~1975-1985: Structured Paradigm
• Structured Systems Analysis, Composite/Structured Design, Structured
Programming, Structured Testing
• Lead to major improvements for software industry.
• But only good for small programs (say, 5,000-50,000 lines of codes)
• Not scale well with today larger programs (say, 500.000-5,000,000 LOC)
• Not so good in software maintenance aspects, (for instance, because of the
separation of action-oriented and data-oriented in structured paradigm).
– Object-Oriented Paradigm
• An object is a unified software component that incorporates both data and
actions that operate of those data.
10
Scope of Software Engineering
Structured Paradigm
Object-Oriented Paradigm
• Requirement Phase
• Specification (Analysis) Phase
• Integration Phase
• Maintenance Phase
• Requirement Phase
• Object-Oriented Analysis
Phase
• Planning Phase
• Object-Oriented Design Phase
• Object-Oriented
Programming Phase
• Integration Phase
• Maintenance Phase
• Retirement
• Retirement
• Planning Phase
• Design Phase
• Implementation Phase
Comparison of life cycles of structures paradigm and object-oriented paradigm.
11
Object-Oriented Software Development
• Three key words.
– Software
– Development
– Object Orientation
• Let us look at each in turn
12
Software
• Programs
• Documentation during the development of
programs (e.g. specification)
• Primary aids for running the programs (e.g.
user manuals)
• Secondary aids for running the programs (e.g.
key boards overlays)
Software is not just programs!
13
Software Life Cycle
•
•
•
•
•
Software is like humans.
It has a life cycle.
Software in a system is conceptualized first.
It becomes obsolescent at the end.
The period in between is called the software life
cycle.
14
Software Life Cycle Models
•
•
•
•
•
•
•
Build-and-Fix Model
Waterfall Model
Rapid prototyping model
Incremental Model
Spiral Model
Concurrent Development Model
Formal Methods Model
For the first four items, please refer to Chapter 3 of
“Software Engineering with JAVA”, S.R. Schach, McGraw-Hill, 1997.
15
Built-and-Fix Model
• Unfortunately, many s/w products are
developed with built-and-fix model.
• Without specification or any attempt in design,
just build a product, and reworked as many
times needed to satisfy the customer.
• Unsatisfactory for any size of s/w development,
we better specify the various phases of software
process.
16
Why use a life cycle model?
• Life cycle model breaks down the development
process into phases or stages.
• This is because software development is
complex.
• Breaking down the development process makes
it easier to manage.
• Each phase can be performed in various ways.
17
Waterfall Model
Requirement
Changed Requirements verify
Verify
Specification
Verify
Planning
Verify
Design
Verify
Implementation
Testing
Integration
Development
Testing
Operation Mode
Maintenance
Retirement
18
Rapid Prototyping Model
• A rapid prototype is a working model that is
functionally equivalent to a subset of the product
(internal structure is not concerned yet).
• The sole use of rapid prototyping is to determine what
the client’s real needs are, construct the rapid
prototype as rapidly as possible to speed up the s/w
development process.
19
Rapid Prototyping Model
Rapid Prototype
Changed Requirements verify
Verify
Specification
Verify
Planning
Verify
Design
Verify
Implementation
Testing
Integration
Development
Testing
Operation Mode
Maintenance
Retirement
20
Incremental Model
• The s/w product is designed, implemented,
integrated, and tested as a series of incremental
builds, where a build consists of code pieces
from various modules interacting to provide a
specific functional capability.
• It is sometimes necessary to re-specify, redesign, re-code, or at worst, throw away what
has already been completed and start again.
21
Incremental Model
Requirement
Verify
Specification
Verify
Planning
Verify
Architectural Design
Verify
For each build:
Perform detailed design,
implementation,
and integration. Test.
Deliver to client.
Development
Operation Mode
Maintenance
Retirement
22
Spiral Model
• The idea of minimizing risk via the use of
prototypes and other means is the concept
underlying the spiral model.
• A simplified spiral model is as a waterfall
model with each phase preceded by risk
analysis.
– Before commencing each phase, an attempt is made to
control (resolve) the risks. If it is impossible to resolve
all the significant risks at a stage, then the project is
immediately terminated.
23
Full Spiral Model [Boehm, IEEE 1998]
Cumulative
cost
Progress
through steps
Evaluate alternatives,
identify, resolve risks
Determine
objectives,
alternatives,
constraints
Risk
Analysis
Risk
Analysis
Commitment
Prototype 1 Prototype 2
Review
Partition
Risk
Analysis
Risk
Analysis
Prototype 3
Operational
Prototype
Simulations, models, benchmarks
Requirement plan
life-cycle plan
Development Plan
Concept of
Operation
Requirement
Validation
Software
Product
Design
Plan next phase
Integration and Test
Plan
Detailed
Design
Software
Requirements
Code
Unit
Test
Design validation
and verification
Implementation
Acceptance
Test
Integration
Test
Develop, verify
next-level product
24
Software Development
• Software is developed using a life cycle model.
• Just a life cycle model is insufficient for
development.
• We need:
– A broad philosophy
– A set of tools which support the philosophy.
– A language which supports the philosophy.
25
Software Development Paradigm
• A paradigm provides a general approach to
work during each phase of the life cycle model.
• A paradigm is a broad philosophy.
• A paradigm is not a specific model.
26
Some Software Development Paradigms
•
•
•
•
Functional Composition
Logic Programming
Structured Development
Object Orientation
27
Functional Development
• A problem is expressed in termed of a set of
mathematical functions.
– e.g. Double(x) = Add(x, x).
• An algorithm is not specified.
• Language such as Miranda, Gofer, Haskell
support this paradigm.
• Poor execution speed.
28
Logic Programming
• Consists of a problem description only.
– e.g. Factorial(0) = 1.
Factorial(N) = N x Factorial(N -1).
• Doesn’t describe how to solve the problem.
• Languages Prolog & Lisp support this
paradigm.
29
Structured Development
• Also called SASD, SADT & Functional
Decomposition.
• Breaks the system into processes & decomposes
them.
• Languages C, Fortran, Pascal, Cobol, Basic
and a lot more support this paradigm.
• By far the most popular paradigm.
30
Object Orientation
•
•
•
•
Most recent paradigm.
Treats a problem as a collection of objects.
Becoming very popular now.
More and more languages support this
paradigm now.
31
Tools for OO
•
•
•
•
Rambaugh (OMT)
Coad-Yourdon
Booch
UML
32
Languages for OO
•
•
•
•
•
•
C++
Smalltalk
Eiffel
Object C
Object Pascal
Java
33
Software Quality Assessment
• CMM by SEI
• ISO 9000
34